Hi, have you ever had her short size investigated? There is a condition called russell silver syndrome (my son has it) which causes short stature and precocious puberty. Just a random thought but it jumped out at me reading your post.

Precocious puberty is puberty starting under the age of 8 so your Dd hasn't started ultra early. It's unusual to start without other signs first as puberty normally follows certain stages- Tanner stages. I would see a GP but they may just say it's within normal age ranges

I remember this happening to me when I was about 9 or 10, after horse riding and I think it must have been hymen breaking (I did feel a sharp pain) Perhaps that's what's happened to your DD? I hope the doc helped, reassurance if nothing else.

This happened to my DD - she was 9, and is skinny as a rake, tall but totally underdeveloped. She had a tiny bit of bleeding 3 months in a row so I went to the GP. She said that it was very unlikely to be periods because she had no other signs of puberty and that periods are the last thing to happen after breast buds, hips etc....So, she said to keep an eye but she wouldn't do any tests until 6 months of bleeding. She hasn't bled since that trip to the GP, is still not developing and is turning 11 in July!